Cellular devices typically include one or more processors for general and specialized computing tasks, and one or more radios for communication tasks. Other sub-systems may include displays, input/output devices, sensors and GPS. A key constraint of such devices is the small form factor desired by users that complicates specifically the design of the RF subsystems. Antennas need a certain physical size related to the wavelengths they receive or transmit to be effective. Close proximity of other platform elements such as circuit boards, batteries, shielding, and the like can severely impair RF performance. In addition, such proximity also increases undesired RF coupling from the antenna back into the device which can lead to unacceptable spurious radio emissions outside the desired operational frequency bands.
Traditionally, antennas are designed with their surroundings in mind, specifically preexisting passive ground planes. The antenna should be tuned to the presence of such ground planes to operate effectively. Thus, antenna designs that include other non-RF platform components, such as batteries, can be desirable to accommodate surrounding components confined within restricted volumes of handheld and portable devices.